31 equivalent discrete time model our goal is to

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Unformatted text preview: to build the appropriate ÀÊ ´ µ to eliminate ISI. However, notice that what we want eventually are the samples at intervals Ì at the receiver. Therefore, we may choose to build a simpler (practical) filter ÀÊ ´ µ, take samples at intervals Ì , and put a digital filter, called equalizer, at the output to eliminate ISI analog filter as shown below in Figure 4.9. This approach to remove ISI is usually known as equalization. The main advantage of this approach is that a digital filter is easy to build and is easy to alter for different equalization schemes, as well as to fit different channel conditions. 3 If the matched filter demodulation technique is employed, the receiving filter conjugate of ÀÌ ´ µÀ ´ µ. 4 Of course, we should choose one that can be easily built. 4.9 ÀÊ ´ µ is chosen to be the complex Wong & Lok: Theory of Digital Communications HT ( f ) Ik 4. ISI & Equalization HC ( f ) Impulses Equalizer Decision Equalizer HR ( f ) Decision every T AWGN Figure 4.9: Communication system with equalizer HT ( f ) Ik HC ( f ) HR ( f ) Impulses every T colored Ga...
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